Microprocessor 8086 Notes Pdf Free Download

[Quincey Homer]

The8086 microprocessor is an 8-bit/16-bit microprocessor designed by Intel in the late 1970s. It is the first member of the x86 family of microprocessors, which includes many popular CPUs used in personal computers.

The architecture of the 8086 microprocessor is based on a complex instruction set computer (CISC) architecture, which means that it supports a wide range of instructions, many of which can perform multiple operations in a single instruction. The 8086 microprocessor has a 20-bit address bus, which can address up to 1 MB of memory, and a 16-bit data bus, which can transfer data between the microprocessor and memory or I/O devices.

The 8086 microprocessor has a segmented memory architecture, which means that memory is divided into segments that are addressed using both a segment register and an offset. The segment register points to the start of a segment, while the offset specifies the location of a specific byte within the segment. This allows the 8086 microprocessor to access large amounts of memory, while still using a 16-bit data bus.

The 8086 microprocessor has two main execution units: the execution unit (EU) and the bus interface unit (BIU). The BIU is responsible for fetching instructions from memory and decoding them, while the EU executes the instructions. The BIU also manages data transfer between the microprocessor and memory or I/O devices.

The 8086 microprocessor has a rich set of registers, including general-purpose registers, segment registers, and special registers. The general-purpose registers can be used to store data and perform arithmetic and logical operations, while the segment registers are used to address memory segments. The special registers include the flags register, which stores status information about the result of the previous operation, and the instruction pointer (IP), which points to the next instruction to be executed.

The size of the internal registers(present within the chip) indicates how much information the processor can operate on at a time (in this case 16-bit registers) and how it moves data around internally within the chip, sometimes also referred to as the internal data bus.

The Prefetch Unit in the 8086 microprocessor is a component responsible for fetching instructions from memory and storing them in a queue. The prefetch unit allows the 8086 to perform multiple instruction fetches in parallel, improving the overall performance of the microprocessor.

The prefetch unit consists of a buffer and a program counter that are used to fetch instructions from memory. The buffer stores the instructions that have been fetched and the program counter keeps track of the memory location of the next instruction to be fetched. The prefetch unit fetches several instructions ahead of the current instruction, allowing the 8086 to execute instructions from the buffer rather than from memory.

This parallel processing of instruction fetches helps to reduce the wait time for memory access, as the 8086 can continue to execute instructions from the buffer while it waits for memory access to complete. This results in improved overall performance, as the 8086 is able to execute more instructions in a given amount of time.

The prefetch unit is an important component of the 8086 microprocessor, as it allows the microprocessor to work more efficiently and perform more instructions in a given amount of time. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

The Decode Unit works in parallel with the Prefetch Unit, which fetches instructions from memory and stores them in a queue. The Decode Unit reads the instructions from the queue and translates them into micro-operations that can be executed by the microprocessor.

The Decode Unit is an important component of the 8086 microprocessor, as it allows the microprocessor to execute instructions efficiently and accurately. The decode unit ensures that the microprocessor can execute complex instructions, such as jump instructions and loop instructions, by translating them into a series of simple micro-operations.

The Decode Unit is responsible for decoding instructions, performing register-to-register operations, and performing memory-to-register operations. It also decodes conditional jumps, calls, and returns, and performs data transfers between memory and registers.

The Decode Unit helps to improve the performance of the 8086 microprocessor by allowing it to execute instructions quickly and accurately. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

The Control Unit in the 8086 microprocessor is a component that manages the overall operation of the microprocessor. The control unit is responsible for controlling the flow of instructions through the microprocessor and coordinating the activities of the other components, including the Decode Unit, Execution Unit, and Prefetch Unit.

The Control Unit acts as the central coordinator for the microprocessor, directing the flow of data and instructions and ensuring that the microprocessor operates correctly. It also monitors the state of the microprocessor, ensuring that the correct sequence of operations is followed.

The Control Unit is an essential component of the 8086 microprocessor, as it allows the microprocessor to operate efficiently and accurately. The control unit ensures that the microprocessor can execute complex instructions, such as jump instructions and loop instructions, by coordinating the activities of the other components.

The Control Unit helps to improve the performance of the 8086 microprocessor by managing the flow of instructions and data through the microprocessor, ensuring that the microprocessor operates correctly and efficiently. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

1.Address Bus: The address bus is used to send the memory address of the instruction or data being read or written. The address bus is 16 bits wide, allowing the 8086 to address up to 64 kilobytes of memory.

3.Control Bus: The control bus is used to transfer control signals between the microprocessor and other components in the computer system. The control bus is used to send signals such as read, write, and interrupt requests, and to transfer status information between the microprocessor and other components.

The Intel 8086 is a 16-bit microprocessor that can access up to 1 MB of memory. It has two main components: the Bus Interface Unit (BIU) handles bus operations like instruction fetching and memory access, while the Execution Unit (EU) decodes and executes instructions. The BIU contains registers for the code, data, extra, and stack segments as well as an instruction queue. The EU has registers for accumulation, base, count, data, pointers, and flags, and contains an ALU and decoder. It executes instructions from the queued bytes using a pipeline architecture.Read less

The 8086 microprocessor is one of the most important chips ever created; it started the x86 architecture that stilldominates desktop and server computing today.I've been reverse-engineering its circuitry by studying its silicon die.One of the most unusual circuits I found is a "bootstrap driver", a way to boost internal signalsto improve performance.1

This circuit consists of just three NMOS transistors, amplifying an input signal to produce an output signal, butit doesn't resemble typical NMOS logic circuits and puzzled me for a long time.Eventually, I stumbled across an explanation:2 the "bootstrap driver" uses the transistor'scapacitance to boost its voltage. It produces control pulses with higher current and higher voltage than otherwise possible,increasing performance.In this blog post, I'll attempt to explain how the tricky bootstrap driver circuit works.

A die photo of the 8086 processor. The metal layer on top of the silicon is visible. Around the edge of the chip, bond wires provide connections to the chip's external pins. Click this image (or any other) for a larger version.

The 8086 is built from MOS transistors (MOSFETs), specifically NMOS transistors.Understanding the bootstrap driver requires some understanding of these transistors.If you're familiar with MOSFETs as components, they have source and drain pins and current flows from the drain to the source, controlled by the gate pin.Most of the time I treat an NMOS transistor as a digital switch between the drain and the source: a 1 input turns the transistor on, closing the switch, while a 0 turns the transistor off.However, for the bootstrap driver, we must consider the MOSFET in a bit more detail.

The important aspect of the gate is the difference between the gate voltage and the (typically lower) source voltage;this is denoted as Vgs.Without going into semiconductor physics, a slightly more accurate model is that the transistor turns on when the voltage between the gate and the sourceexceeds the fixed threshold voltage, Vth.This creates a conducting channel between the transistor's source and drain.Thus, if Vgs > Vth,the transistor turns on and current flows.Otherwise, the transistor turns off and no current flows.

The threshold voltage has an important consequence for a chip such as the 8086.The 8086, like most chips of that era, used a 5-volt power supply.The threshold voltage depends on manufacturing characteristics, but I'll use 1 volt as a typical value.3The result is that if you put 5 volts on the drain and on the gate, the transistorcan pull the source up to about 4 volts, but then Vgs falls to the threshold voltage and the transistor stopsconducting. Thus, the transistor can't pull the source all the way up to the 5-volt supply, but falls short by a volt on the output.In some circumstances this is a problem, and this is the problem that the bootstrap driver fixes.

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